Physico-chemical changes in cladodes of Opuntia ficus-indica as a function of the growth stage and harvesting areas

The physicochemical properties of cladodes Opuntia ficus-indica (OFI) vary widely during maturation. However, few studies have been performed to evaluate changes in chemical characteristics on the pad depending on the maturity stages. Chemical proximate analysis like the content of total sugars, protein, dry matter, pH, conductivity and ash, depending on the variation of weight of the pad and the growing region was done to determine the changes of characteristics of nopal. Significant changes in physicochemical properties were observed among harvesting sites and during the growing stages. The principal component analysis was then performed to evaluate the relationship between harvesting sites, growth stages, and physicochemical properties. Results highlighted that Sidi El Aidi can be categorized as a poor ecotype among the studied ecotypes, besides, overall harvesting sites pH and proteins had a significant negative correlation with ash, total sugars, reducing sugars, conductivity proteins decrease with increasing age of nopals while total sugars, reducing sugars, and ash content showed the opposite trend. The high total sugar content, minerals of nopal pad (weight higher than 200 g) and proteins (weight lower than 200 g) could be an interesting source of these important components for human diets and also could be used in food, cosmetics, and pharmaceutical industry.

Back-gated spray-deposited carbon nanotube thin film transistors operated in electrolytic solutions: an assessment towards future biosensing applications

We report on back-gated carbon nanotube (CNT) thin-film transistors (CNTFETs) and their performance in electrolytic solutions to assess their suitability for future application as biosensors. Spray-deposited CNT networks were used as the sensitive active layer which offers the opportunity for integration on flexible sensing platforms at low-cost. We characterized the transistors' behavior in electrolytes by analyzing the response to different KCl solutions and buffers over a wide pH range. We observed a linear response of the drain current upon changing the pH in low molarity buffers and obtained an exponential dependence on the salt concentration of the electrolyte. These responses can be attributed to electrostatic gating effects that go along with shifts in the threshold voltage. Even though a lot of effort has been put into understanding the biosensing mechanism a detailed theory is still missing. Back-gated CNTFETs operated in electrolytic solutions can be a further tool to investigate and clarify the existing unsolved phenomena.